The present invention relates to a device for driving a piezoelectric vibrator.
Conventionally, a piezoelectric vibrator is designed to be driven by a device including an AC power supply which is variable in frequency. This concept or structure is based on the fact that the resonance of a piezoelectric vibrator causes its effective vibration upon application thereto of a suitable frequency of an AC signal. Such structure has been shown in Japanese Patent Publication No. 50-26391 which was published after examination in 1975. In the device shown in this document, the output frequency of an AC power supply is adjusted so as to establish an in-phase relation between the current and the voltage of electric power supplied to a piezoelectric vibrator. Similar structure is also shown in Japanese Kokai 59-87078 published in 1984 without examination. A piezoelectric vibrator is used for vibrating a mirror in the form of a plate member to thereby remove water drops thereon as disclosed in Japanese Kokai 62-238149 published in 1987 without examination.
However, the foregoing piezoelectric vibrator is expanded and contracted repeatedly in such a manner that the vibrator is bent into a curvature having a considerable radius in opposed directions, thereby generating minute crazes in the vibrator in a short time. This leads to the degradation of the piezoelectric vibrator. In addition, if such a piezoelectric vibrator is secured to a mirror, excessive stress will be applied to the mirror, thereby generating cracks therein.